subnetting

[carl_townshend]

Hi all, when subnetting, I know for the host portion of the address we need to leave 2 bits, but when we look at the network portion, do we need to leave 2 bits for the network? i thought its only for the host portion ? as we can use subnet zero

[williamsdo]

Hi, you are correct two bit must remain for the host portion of the subnet mask, ANDing requires a mix of 1 and 0's to determine the host's address. As for the network we know it can be all 1's in the network portion and with subnet zero available I do believe you can use all the bit's in the network protion. Maybe an expert can add additional information for you. HTH

[craig.eyre]

Hi Carl,

I think you answered your own question in that we can now use subnet zero, eliminating the 2 networks that we use to save. Depending on your hardware and IOS versions you may not be able to use subnet zero.

Hope this helps.

Craig

[l.mourits]

Actually, there is a RFC (or is it still in draft?) about using /31 host adressing for point to point links, so even for the host part your statement is no longer completely true ;-)